It is known that the sensitivity of a silver halide photographic light-sensitive material obtained by spectral sensitization, i.e., spectral sensitivity, is influenced both by the structures of sensitizing dyes used and by various properties of emulsions, such as silver halide composition, crystal structure, crystal habit, silver ion concentration, hydrogen ion concentration and the like, as well as by photographic additives present in emulsions. Further, the sensitizing dyes cannot remain in the processed light-sensitive material to cause discoloration. In particular, with a recently increasing demand for rapid processing, it is important that the sensitizing dyes not remain in the processed light-sensitive material to cause discoloration and do not cause fog in short time processing (usually several seconds to several tens of seconds).
In general, the spectral sensitivity of a light-sensitive material can be broadened to a prescribed spectral wavelength region by using one sensitizing dye. However, the combined use of two or more different sensitizing dyes (supersensitization) frequently results in a lower sensitivity compared with the sensitivity obtained with their individual use. Therefore, when super-sensitization is attempted using a combination of sensitizing dyes, groups of dyes which can be used in combination must be carefully selected for compatibility.
Light-sensitive silver halide emulsions exhibiting a high spectral speed and excellent sharpness have recently been developed using tabular silver halide grains with high aspect ratios (ratios of grain diameter to grain thickness). However, these silver halide emulsions have the disadvantage that sensitivity and contrast are greatly varied by latensification after exposure even if the emulsions are spectrally sensitized by commonly employed sensitizing dyes (e.g., benzimidazole) under optimum conditions, with the result that normal images cannot be formed. In addition, storage of those materials for a long period of time increases fog and reduces sensitivity. Japanese Patent Application (OPI) Nos. 108526/83 and 113927/83 disclose technique for spectral sensitization of tabular silver halide grains, but these prior art techniques do not provide satisfactory photographic properties such as sensitivity.